C9orf72 and frontotemporal dementia: Alternatively, reduced C9orf72 mRNA levels in a range of patient tissues and patient-derived cell lines2,14-18 and reduced C9orf72 protein levels in the frontal cortex of C9ALS/FTD patients19,20 suggest loss-of-function by C9orf72 haploinsufficiency may also contribute to C9ALS/FTD.